Electron discharge device



DEC. 31', 1940. BRETT 2,227,062

ELECTRON DISCHARGE DEVICE Filed Feb. 8, 1937 INVENTOR GEORGE FAIRBURN BRETT BY #5. KM

ATTORNEY Patented Dec. 31, 1940 ELECTRON DISCHARGE DEVICE George Fairburn Brett, London, England, assignor to Radio Corporation of. America, a corporation of Delaware Application February 8, 1937, Serial No. 124,702 In Great Britain February 8, 1936 8 Claims. (01. 250-475) This invention relates to electron discharge devices and more particularly to electron discharge devices of the electron multiplier type, i. e. of the type wherein a primary electron stream from a cathode of any suitable type is magnified or amplified in one or more steps by utilizing the phenomenon of secondary emission.

Numerous forms of electron multipliers have been proposed but most of the hitherto proposed forms have involved the defect of complication bulk or have fallen short of what is required as respects efiiciency by reason of insufflcient accuracy of focussing of incident electrons upon the secondary emitting electrodes intended to receive said electrons.

The object of the present invention is to provide an improved electron multiplier of simple and relatively small construction and capable of high efiiciency.

According to this invention an electron multiplier device comprising in cascade a plurality of Y electron sources one of which is a primary source and the other or others of which is or are secondary emitting, is characterized in that said sources form parts of what are in effect electron guns each of which projects its electronbeam (primary or secondary as the case may be) to the next electrode in the device.

The invention is illustrated in the accompanying drawing in which Fig. 1 shows schematically one embodiment of my invention showing a plurality of electron guns, while Fig. 2 shows schematically a modification of one of the guns.

Referring to Fig. 1 which shows schematically one way of carrying out this invention an electron multiplier comprises within an evacuated envelope a series of electron guns Gl, G2, G3 and an output electrode A all arranged side by side. Each gun comprises an accelerating anode AA], 40 AA2, AA3 and an electron source Cl, 02, C3

(primary or secondary as the case may be) in the form of an approximately rectangular depression in an otherwise planar electrode. All the accelerating anodes are in one plane AAI, AAZ, AA3 and 45 the planar electrodes of which the electron sources form part are in a second plane with one another and with the output electrode A, the second plane being parallel to the first plane. In Fig. 1 there are three electron guns of which two (G2, G3) have secondary electron sources and one (GI) has a primary electron source. The primary electron gun may be either thermionic or photoelectric, the source of electrons Cl being at the bottom of the rectangular depression or pocket formed in or behind the apertured plate-like electrode which, as shown, is closely behind the accelerating anode AAI also in the form of an apertured plate. The second electron gun is precisely similar to the thermionic electron gun except that the cathode surface is not thermionic but is prepared with caesium or other material of low work function so as to be capable of secondary emission. The third electron gun is similar to the second electron gun. v Corresponding parts of all the guns are co-planar 10 and the output electrode A which is in the form of a simple plate, is co-planar with the apertured electrodes behind which the electron emitting surfaces are positioned. All the guns are equally spaced from one another the spacing between the 15' last gun and the output anode being the same as that/between consecutive guns. Increasingly positive potentials are applied to successive guns and to the output electrode the step of potential increase between one gun and the next being of the order of 300 volts in each case. A magnetic field generated by means not shown is applied to the whole system in a direction perpendicular to the direction-s in which electron beams would (were there no applied magnetic field) be pro- 25 jected from the various guns, and the whole arrangement is such that the electron beam from the first gun moves (as indicated in chain lines) in a substantially semi-circular path to a focus upon the electron emitting secondary cathode of 30 the second gun G2; similarly there is emitted from this gun an electron beam which moves in a semi-circular manner to the cathode of the third gunG3 which in turn emits an electron earn which passes semi-circularly to the output 35 anode A.

Although with the arrangement above described the electrostatic fields will not be completely uniform each gun may be caused to emit an electron beam which can be focussed with quite good accuracy upon the electron emitting surface of the next gun.

In a modification of the above described arrangement, instead of forming the cathodes in the form of rectangular pockets or depressions in 5 planar electrodes, each cathode is constituted (as illustrated in Fig. 2) by a separate plate-like electrode C arranged behind the aperture in a planar electrode P which is in turn behind the accelerating anode AA. Each separate cathode may (as shown in Fig. 2) be permanently connected to the plate-like electrode P immediately behind which it is situated, or separate leads may be provided to said electrodes in the case of one or more of the electron guns. The advantage of providing separate leads is that desired controlling biases may be applied between "the separate cathodes and the plate-like electrodes immediately in front of them so that the said platelike electrodes may be used as control electrodes for modulating the various emitted electron beams.

What I claim is:

1. An electronic device comprising a plurality of electron guns each comprising two apertured electrodes mounted in a line, with the axes of the guns parallel to each other, and an output elec-- trode in line with the electron guns and perpendicular to the axes of the guns.

2. An electron device comprising a plurality of cathodes extending along a predetermined path and lying in the same plane, an apertured electrode positioned in register with each of the cathodes, an output electrode lying along the predetermined path and in the same plane as the apertured electrodes, and means to provide a magnetic field perpendicular to the predetermined path.

3. An electron device comprising a plurality of cathodes extending along a predetermined path and lying in the same plane, a plurality of apertured electrodes positioned in register with each of the cathodes, an output electrode lying along the predetermined path and in the same plane as one of the apertured electrodes, and means to provide a magnetic field perpendicular to the predetermined path.

4. An electron device comprising a plurality of cathodes extending along a predetermined path and lying in the same plane, a plurality of apertured electrodes positioned in register with each of the cathodes, an output electrode lying along the predetermined path and in the same plane as one of the apertured electrodes, means to provide a magnetic field perpendicular to the predetermined path, and a connection from each cathode to one of its associated apertured electrodes.

5. An electron device comprising a plurality of secondary emissive cathodes positioned adjacent to each other and lying in the same plane, means to set up a magnetic field, the lines of force which are parallel to said plane, an apertured electrode element in register with one of said cathodes for cooperating with said magnetic field to focus electrons from said one of said cathodes onto a next adjacent cathode, and a further apertured electrode element in register with said next adjacent cathode for cooperating with said magnetic field to focus electrons from said next adjacent cathode onto a second adjacent cathode.

6. An electron device comprising a plurality of secondary emissive cathodes positioned adjacent to each other and lying in the same plane, means to set up a magnetic field, the lines of force of which are parallel to said plane, an apertured electrode element in register with one of said cathodes for cooperating with said magnetic field to focus electrons from said one of said cathodes onto a next adjacent cathode, a further apertured electrode element in register with said next adjacent cathode for cooperating with said magnetic field to focus the electrons from said next adjacent cathode onto a second adjacent cathode, an output electrode, and an apertured electrode element in register with said third named cathode for cooperating with said magnetic field to focus electrons from the third named cathode onto the output electrode.

'7. An electron device comprising a first electron gun having a hollow cathode comprising a planar electron emissive surface and having a restricted discharge opening, a second similar electron gun wherein the emissive surface is secondary electron emissive, said emissive surfaces lying in the same plane, and the axes of both of said guns being parallel, and magnetic means to focus electrons from said first electron gun onto said secondary electron emissive surface.

8. An electron device comprising a first electron gun having a hollow cathode comprising a planar electron emissive surface and having a restricted discharge opening, a second similar electron gun wherein the emissive surface is secondary electron emissive, said emissive surfaces lying in the same plane, and the axes of both of said guns being parallel, an output electrode, and magnetic means to focus electrons from said first electron gun onto said secondary electron emissive surface and to focus electrons from said secondary electron emissive surf-ace onto said output electrode.

GEORGE FAIRBURN BRETT. 

